A compression ignition type internal combustion engine is known in the art which arranges a particulate filter for trapping particulate matter in exhaust gas inside an exhaust passage. The particulate filter is provided with alternately arranged exhaust gas inflow passages and exhaust gas outflow passages and porous partition walls which separate these exhaust gas inflow passages and exhaust gas outflow passages from each other. The downstream ends of the exhaust gas inflow passages are closed by downstream side plugs, while the upstream ends of the exhaust gas outflow passages are closed by upstream side plugs. Therefore, exhaust gas first flows into the exhaust gas inflow passages, next passes through the surrounding partition walls, and flows out to the insides of the adjoining exhaust gas outflow passages. As a result, the particulate matter in the exhaust gas is trapped on the partition walls and is suppressed from being discharged into the atmosphere.
In this regard, if the amount of the particulate matter on the particulate filter becomes greater, pressure loss of the particulate filter gradually becomes larger. As a result, engine output is liable to fall. Therefore, in this internal combustion engine, PM removal processing which maintains the particulate filter in an oxidizing atmosphere while making the temperature of the particulate filter rise is performed. Due to this, the particulate matter is burned off from the particulate filter.
In this regard, exhaust gas contains unburnable ingredients called “ash”. This ash is trapped together with the particulate matter on the particulate filter. In this regard, even if PM removal processing is performed, the ash will not burn or be vaporized but will remain on the particulate filter. For this reason, as the engine operation time becomes longer, the amount of ash on the particulate filter gradually increases and the pressure loss of the particulate filter gradually becomes greater. As a result, even if the PM removal processing is repeated, the engine output is liable to decrease.
Therefore, a particulate filter is known in the art which forms through holes in the downstream side plugs to enable ash to flow out from the particulate filter through the through holes (see PLT 1). In this PLT 1, if the engine operating time becomes longer, the through holes become closed by the particulate matter. If the through holes are closed, the particulate filter can trap particulate matter in the same way as a conventional particulate filter which does not have through holes. Next, if PM removal processing is performed, the particulate matter which closed the through holes is removed and the through holes are opened. As a result, the ash on the particulate filter is discharged from the particulate filter through the through holes.